The present invention relates to a frame for a chair, comprising a seat part and a backrest part, the seat part being supported on a support part provided with a support arm and connected in articulated manner to the backrest part, whilst on the knee side the seat part is supported by means of a joint and on the backrest side by a backrest strut via a spring element on the support arm.
Chair frames having a seat part and a backrest part are known in a number of different constructions. In one frequently used chair frame in which the seat part and backrest part can be pivoted rearwards and downwards, the seat part is articulated to a support arm on the knee side. The support arm is part of the foot or base frame of the chair having a vertical support column, to which the support arm is fixed.
The seat part is connected in either a fixed or an articulated manner to the backrest part. In the latter case the back part is supported by means of a compression spring element, usually a gas pressure spring, on the support arm. This chair frame has been produced in large numbers and has proved satisfactory. However, the manufacturing costs are relatively high, because the forces exerted by a chair user on the seat part and the back part and which are transferred via the support arm into the base frame are considerable and the parts require frequent replacement. In chairs with a pivotable seat part and/or a pivotable back part, it is necessary to connect these two parts by additional connecting elements to the support arm. As these additional connecting elements must be housed with a minimum amount of space being consumed, forces can occur thereon, whose magnitude can significantly exceed the body weight of the chair user. In particular, the spring elements must be designed for such additional forces, which increases manufacturing costs and therefore the chair costs.
The Applicant has developed a chair (EP-A-264029), in which the backrest side support of the seat part and the back part does not take place directly on the spring element, but instead occurs via a movable slide, which is displaceably guided in a parallelogram linkage articulated to the support arm and which is connected to one end of the spring element, whose other end is supported on the parallelogram linkage. Thus, it is possible to significantly reduce the forces on the spring element, so that the latter can be made much smaller. Another advantage is that in the case of this chair frame there is no longer any need to make an adjustment with regards to the differing weight of the chair user. In addition, the connecting elements between the seat part, the back part and the support arm can be kept small, so that the volume required for housing these elements under the seat can be kept correspondingly small.